Method of bluing coal



March 2 1943.

G. P. HAM ETAL METHOD 0F BLUING COAL Filed Jan. 9, 1941 5 Sheets-Sheet llvENToRs March 2 1943. G. P; HAM rAL METHOD oF BLUING co'AL Filed Jan.9, 1941 5 Sheets-Sheet 2 w uam. Ob

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Filed Jan. 9. 1941 5 Sheets-Sheet 4 IN VENT ORS ,HH n 7 .u n... ...n u.l ...www -...1 JT H M F 2 m r f d 4 N r M a ABYl egg-f March 2 1943'.

G. P. HAM ETAL METHOD 0F BLUING coAL 5 sheets-sheet 5 Filed Jan. 9, 1941A INVENTORS Patented Mar. 2, 1943 Unire STT S 'rr ortica METHOD F BLUINGCOAL ration of Maine Application January 9, 1941, sei-iai No. 373,712 4claims. (cl. coe-131) The present invention relates to a method ofelectrolytically depositing iron blues upon coal surfaces.

The principal object of the present invention is to carry out the abovemethod under such and soluble ferrie salts Where coal was subjected to aspray of, or immersed in, the combined solu tions. 'These methods,lwhile ordinarily satisfactory, are not always competitive from thestandpoint of cost as there are a number of' cheaper ways available toapply a distinctive blue color to a coal surface.

A study of the mechanism of the coloring reaction involved in iron blueshas led to a number of very interesting discoveries, some of which arecontradictory to published data. y

It was, therefore, one of the objects of the invention to exhaustivelystudy this subject in order to determine optimum conditions under whicha satisfactory iron blue color could beobtained on a coal surface atminimum cost.

It has been discovered that among .the iinportant considerations inaccomplishing the above object, are such items as particular ierriccompounds, reactant ratio and dilution, reaction temperature, the pli-Iof the reacting solution and the carrying out of the reactions under theinfluence of D. C. electrical potential, While the coal is, or is incontact with, Vthe negative electrode. This last feature is by far themost important in that when thereaotion is carried out `electrolyticallyunder controlled conditions, the speed of formation of the iron blue onthe coal surface is materially increased. This being true, other factorsmay be adjusted to suit commercial conditions, taking advantage of thespeed conv trol aiioided by the electrical impulse.

'Ihe invention, therefore, contemplates in one of its broad aspects theelectrolytic deposition of iron blues on coal from solutions of alkalimetal ferricyanides and ferrie nitrate, chloride or 0 sulfate, Whilemaintaining the coal to be-colored constantly within unidirectionalelectrical :Lcir cuit. While conditions of choice of reactants? theirdilution, the temperature of the reaction'l and the pH are allimportant, yet theserare secondary as compared with the use of anelectrical circuit.

The invention further contemplates the novel steps of the methods andconditions under which the steps are carried out, all as more fullyhereinafter described and diagrammatically shown vin the accompanyingrdrawings.-

In the drawings:

Fig. 1 is a graph showing the result oi-'loluing time asv compared witha control plotted against a ratio of ferricyanide and ierric nitrate;

Fig. 2 isa graph showing the eiect oi ternperature on bluing time Fig.v3is a graph showing the result of sub-Ay jecting coal to an electricalpotential while sube' jected to the bluing reagent; 'Y

Fig. 4 is a diagrammatic 'representation of a piece'of coal used as anegative electrode in Athe bluing bath; A Fig; 5 is a diagrammaticrepresentation -of`a piece of coal used as a positive electrode in thebluing bath; y

Fig. 6 is av sectional elevation of an apparatus adapted to 'carry outthe present invention;

Fig. 7 is a plan View of the device of Fig. 6;

Fig. 8 is a sectional view along the'line 8-8 of Fig. 7;

Fig. 9 is a sectional end view of a modified form of device.

At' the outset, it has vbeen discovered after a considerable andextended experimentation `that anthracite coal varies inY its electricalconductivity to a tremendous extent. For' example,y samples of coal fromdifferent collieries have"y been found to have electrical resistance (D,C)

through samples about two inches. thick over a range from ohms to ashigh as 13 million ohms.` The present invention is particularlyapplicable to v'anthracite coal having an electrical resistance (D. C.)of from 100 tov 800,000 ohms,

for it is within this range that the apparent ef fect of theelectrolytic method is most noticeable.

The color of a Iilm of iron blue on coal is a function of the appliedlayer thickness. This has been denitely determined by spectrophotometric analysis. The amount produced is also a 'function'of time andsolution temperature. As processing times increase, the color of theapplied film goes through the shades of gold, bronze, purple, violet,blue, blue-green, green and green-yellow. Beyond vthis point, second'order` interference results.

Indeter'rnining the effect of various 'conditions upon the` bluingo'fcoal by' the herein described methods, matched samples'of freshlyfractured coal pieces were obtained by cracking a lump of coal and usingthe two matched faces, one for the control and the other for theexperiment. This method of experimenting was determined to the best byreason of the fact that initial work determined that unless the surfaceto be treated Was a freshly fractured one, the results werenonuniformand undependable. After .treatment of both surfaces for theprescribed time-period, the pieces were quickly water washed to stop thereaction and then dried in a current of air.

A 1% solution of reactants was arrived at as representing optimumconditions, both from the standpoint that considerable-volume wasrequired to treat large masses of coalland-also Afrom the standpointthat commercial practicehas adopted this concentration as a standard.

Experiments have demonstrated that of the soluble ferric salts, thenitrate, chloride and vsul fate give the best results with alkali metalferricyanides in the order named. Of these three, the ferric nitrate wasoutstanding in that it required less time to 'produce a desired colorthan `with either the chlorideor `the sulfate. This having beendetermined, further experiments Iwere made only with -the nitrate. As tothe alkali metal ferricyanide, the sodium salt Vis preferredbecause ofcheapness.

In-an effort to determinethe-effect .on bluing whenvarying-proportionsof the component solutions, it hasbeen `found lthat byiincreasing theratio of 1% ferrie nitrate-solution to 1% ferricyanide solution througha range of from `1:.1 to 1:6,the bluing time decreased at a 1:2-ratiobut then became gradually decadentat higher ratios because of areduction inpH value.

For instance, a certain coal'blued inthe 1:1 contro1 bath in 15 seconds,-while a similar vtype coal treated in a 1:2 ratio solution Aofyferricyanide vto ferrie nitrate blued in 13 seconds. Further changessuch asa ratio of .1 :5 required 15 seconds longer to blue than thecontroler 30-sec onds-in all. Fromthe graph of Fig. 1, the elect of thisdilution is clearly shown `where a ratio of 1 :2 maybeconsideredfasoptimum.

As showingl the effect of temperature variations, certain coals bluedwith a control using 1:2 ratio solution at 23 C. in 15 seconds. Whenusing a matched surface, and increasing the temperature ofthe bath, thebluing time to obtain the same color decreased. For instance,`where-theitemperature of `the vbluing solution was higher thanthecontrol, or 33C., the time required .to match the Vcontrol color wasfour secondsfaster or only eleven seconds. Again, when the temperatureof the bluing solution .was 51 C., only four seconds was'required tomatch the color of the control specimen.

-On the contrary, when the temperature of the solution was 13 C.,witrequired 12 seconds longer to reach the color acquired by the control,or.27 seconds. Y

The pH value of the mixed solution is a factor toward the speed ofbluing coal as it controls the formation of the fferri ferricyanideions'which are essential in the process.

As illustrating this, it Yhas been determined-that the pI-l` value of abluing solution, thatis, Oneipart by volume of 1% alkalimetal'ferricyanide and 1 part by volume. of 1% ferrie nitrate-solutionis 2.3 at.25 C. .Lowering this value by the-additionof a mineral acidcauses a decided -slowing of the bluing reaction. For instancawhenthe pHwas made .1.3 .bynitrcacidthe bluing-time of a bath which had previouslybeen 15 seconds was in- .imum bluing time is to be observed, the pHshould not be adjusted beyond that normally obtaining `with the -desiredproportion of ferricyanide to ferric nitrate.

Theabove study was thought necessary in order to determine the mostfavorable conditions lead- `ing up to the bluingof coal in the shortestspace of time Vso that these conditions could be used as a-standard todetermine the effect of an electric field upon the reaction.

Fig..3 showsfthe effect as to bluing time While carrying out thereaction within a D. C. electrical circuit as compared withanon-electrical control.

" In `theseexperiments, a bath of freshly mixed 1% sodium .ferricyanideand 1% ferrie nitrate,.in the proportion of 1:2.at a temperature of 23C. was used. Thecoal piece-to be tested was made the negative electrodewhile a positive electrode was formed of a sheet of aluminum immersed inthe solution as shown in Fig. 4.

From Fig. 3, it will be noted-that when the reaction was carried outunder a potential of `as little. as three volts, a considerable decreasein the bluing time was obtained over a non-electrical controlto obtainthe samedegree of color. The lcgurrent potentials mentioned on theligure are n From .this-figure, it will be noted that as the potentialincreased generally speaking, the bluing time decreased. While there issome variation in the uniformity of this decrease Aas potentialincreases, `this is undoubtedly due to the factthat the particularpieces of coal tested variedin their electrical resistance.

When the polarity of the coal piece and the aluminum electrode vwasreversed -as in Fig. 5. no bluing ywas obtained, even after an extendedperiod.

VvAsa result o1 the discovery that color could not be obtained at allunless the coal piece was the negative electrode, it was notsurprisingto find that when alternating current was substituted fordirect current, no bluing was obtained.

.From the above, it has been definitely detei-mined that, all thingsbeing equal, if the coal piece is blued while being subjected to theinuence. of aD. C. electrical circuit where the coal is, Aor isincontact with, the negative electrode, the bluing time may be decreasedin reaching a required standard of color as compared to a conipletelynon-electrical method.

In adapting the above experimental procedures to commercial operations,the apparatus shown in Figs. 6 to 9 were used. This apparatus consistsgenerally of an inclined shaker chute actuated by a cam driven from aspeed controlled motor, the rebound being caused by a spring. Reagentnozzles are provided at various points above the surface of the coalchute and connected toa'suitable source of mixed reagent.

Onezforxn of device is shown in Fig. 6 as consisting of a trough lsupported upon a'seres of rollers 2, a shaking action being securedthrough rotary cam fingers 3 against cam rollers 4. A

chain connects a motor-driven sprocket 6 with the sprocket 'I whichactuates the cam lingers. Rebound is accomplished by means of the springThe bottom of the trough I is faced with a metal sheet 9 and overlaidwith dielectric strips III such as a molded plastic or the like. A busbar II extends between the stationary sides I2 of the apparatus, theformer having depending therefrom a series of electrodes I3. The bus barII is made the negative terminal of a direct cur rent circuit While themetal plate 9 is made the positive terminal.

The reagent is supplied through pipe I4 while air under compressionenters through jet I5 so as to develop a good spray projected in thedirection 'of travel of the coal pieces.

Coal I6 is moved down a stationary chute Il into a trough I. Due to thefact that the trough is being constantly shaken, the coal pieces movestepwise down the former.`

As shown in Fig. 6, each piece of coal completes the circuit between thedepending negative electrode I3 and the metal plate 9, when the coal iswet with the reagent spray although the coal itself is out of contactwith the plate 9. As there are a large number of these dependingelectrodes, each piece of coal in its travel down the chute iscontinuously bathed in reagent and in an electrical field. Excessreagent flows from the bottom of the trough I into the tank I8 Where itis either disposed of or recovered for reuse. The coal drops off the endof trough I and passes under water spray I9 so as to com- Ypletelyremove excess reagent. The coal is then air dried.

A modified form of apparatus is shown in Fig. 9, which differs from thatof Figs. 6, '7 and 8 only in that the overhead electrode takes the formof a series of continuous reagent streams 2D emerging from pipe 2'Iconnected to the supply manifold 22. The manifold is connected to asource of direct current as the negative electrode. In this way, thepieces of coal as they progress down the chute are constantly bathed inliquid and due to the fact that the streams are unbroken, are alsoconstantly in the electrical circuit.

In one experiment, the apparatus of Fig. 9 was used in which, however,instead of the continuous unbroken streams of reagent 20, the reagentwas sprayed as individual particles upon the coal, the spray nozzlesbeing the negative electrode. After repeated failures to decrease thebluing: time of coal in this apparatus over a s imilar non-electricalmethod, using voltages of from a fraction of a volt to 700 volts, it wasdefinitely determined that the reason for this failure was that therewas no ow of current between the spray nozzle and the surface on whichthe coal rested. Regardless of the ineness of the reagent spray or thedistance between the point of emergence of the spray and the coalsurface, it was impossible to establish a circuit by this method. It wasonly when the stream of reagent Was continuous that the circuit wasestablished and under these circumstances, no difficulty was'encountered in decreasing the bluing time. The optimum current strengthwas found to be between one and 50 volts. Even a fraction of one amperewas found to be suicient, it being only necessary to cause a currentflow at the voltage used.

The above has clearly demonstrated the fact that to be bluedelectrically, the coal must not only be the negative electrode butit`must be continuously in the electrical circuit. Under thesecircumstances, less time is required to reach a standard color with aferricyanide-ferric salt mixture than where a non-electrical conditionexists.

While the invention has been shown and described with specific referenceto specific embodiments, it is to be understood that it is not to belimited thereto but is to be construedy broadly and restricted solely bythe scope of the appended claims.

WeV claim:

1. A method of bluing coal which includes applying thereto a solutioncontaining a ferricyanide and a ferric salt while continuously passing adirect current from a positive electrode, through the solution, to thecoal, the latter serving as the negative electrode.

2. The method of claim 1 in which the ratio of ferricyanide to ferriesalt is substantially 1:2.

3. The method of claim 1 in which the current potential is from one tofty volts.

4. The method of claim 1 in'which the ratio of ferricyanide to ferricsalt is substantially 1:2 and the current potential is from one to fiftyvolts.

GARNET P. HAM.

ROBERT B. BARNES.

